Plasma encapsulation for electronic and microelectronic components such as oleds

ABSTRACT

The invention relates to a plasma encapsulation for electronic and microelectronic components such as OLEDs. However, a conventional standard plasma coating process is not used; instead, an especially gentle plasma coating process which does not cause any damage to sensitive components such as an OLED is used, such as the pulsed method or the “remote” or “after glow method.”

[0001] The invention relates to a plasma encapsulation for electronicand microelectronic components such as OLEDs.

[0002] Components manufactured with materials that are chemicallyunstable in the atmosphere must be protected against contact with theatmosphere.

[0003] A typical example for semiconductor components that must beprotected against contact with the atmosphere are organic light-emittingdiodes (OLEDs), which are generally manufactured with materials that arenot resistant to environmental conditions. Other examples aresuperconductive components based on YBCO (“YBCO” stands for yttriumbarium copper oxide, which is a superconductive material) thin films (L.Mex et al. in Applied Superconductivity, 1997. Proceedings of EUCAS 1997Third European Conference on Applied Superconductivity volume 1, pages161-164) or electronic components on an organic basis, such as organicfield effect transistors (OFET).

[0004] Incompatibility with the atmosphere places particular demands onthe thickness of encapsulation. In addition, materials that are unstablein the atmosphere are often characterized by high reactivity to manyother materials. This means that chemical compatibility between thematerials used for encapsulation and the component to be protected mustbe ensured. Moreover, the thermal resistance of the functional organicmaterials used in OLEDs is limited. Consequently, another requirementfor the encapsulation process is that it must be performed at the lowestpossible temperatures. This is especially the case with OLEDs,

[0005] which are generally only resistant up to temperatures of approx.100° C.

[0006] Another important requirement, in addition to thermalcompatibility during the production process, is resistance to thermalstress during the use of the display. Consequently, materials ofparticular interest for encapsulation are those that exhibit a suitablethermal conductivity for heat removal, thereby protecting the deviceagainst overheating.

[0007] Another requirement for encapsulation is added when OLEDs are tobe applied to flexible substrates, such as polymer foils or chip cards.In this case, the encapsulation must also be flexible.

[0008] In principle, thin-layer processes and, in particular,plasma-supported CVB (chemical vapor deposition) processes are suitablefor use with such encapsulation processes. It is known that they can beexecuted in such a way that the temperature requirement (T<100° C.) isfulfilled. Because of the strong intrinsic integration of plasma layers,they possess thermal conductivity, which is used in a targeted mannerwith DLC (diamond-like carbon) a-C:H coatings for heat removal oncomponents. In addition, plasma processes provide pinhole-free coatings,which are also flexible. Furthermore, plasma-supported processes arewidely used in semiconductor technology and are easily automated.Nonetheless, it has not been possible to date to use such processes inthe coating of OLEDs. In the professional sphere, it is believed thatradiation damage triggered by the photons in the plasma causes damage tothe OLEDs (U.S. Pat. No. 5,771,562, Sp. 1, Z. 37/39; U.S. Pat. No.5,686,360, Sp. 2, Z. 18/20; U.S. Pat. No. 5,747,363, Sp. 2, Z. 14/17).

[0009] This is explained by the fact that plasma contains photons whoseenergy is sufficient to split chemical bonds. When these photonsinteract with the compounds of the organic light-emitting diodes, achemical modification of this material takes place. However, because thelight-emitting properties of these materials depend very precisely onthe chemical structure of the materials used, such modification, whichis poorly defined in chemical terms, heavily affects or completelyeliminates the light-emitting properties.

[0010] Although plasma-polymerized coatings for the coating of OLEDs areproposed in several printed publications, such as WO 98/47189, WO98/59356 and WO 99/02277, these publications only make reference toconventional plasma-coating techniques, such as those used as standardprocesses in the semiconductor industry. This means that radiationdamage, which is described in the US publications and is, in fact,unavoidable, is accepted and, for the reasons cited above, no OLEDs withtechnically appealing serviceable lives can be manufactured in themanner proposed therein.

[0011] The encapsulation of OLEDs with the aid of “roof structures” madefrom atmosphere-proof materials is known in the art. Glass is used inmost cases. However, it is also known that metals can be used for thispurpose. These roof structures are bonded to the substrate onto whichthe OLED layer systems are applied and cover the entire OLED layerstructure. An especially advantageous method of encapsulation isdescribed in DE 19943148.5 (as yet unpublished). It describes the use ofso-called glass caps, which contain cavities in the area in which theOLED layer structure is covered. These cavities are easily manufacturedto any shape and depth by means of sand blasting, for example. In allcases, special attention is paid to the bonding technology used to bondtogether the substrate and the roof structure. For example, “glasssoldering” is used, i.e., the bonding of glass parts by means of glasssoldering (WO 97/46052). As this requires high temperatures, organicadhesives such as

[0012] epoxies are also used to encapsulate organic diodes. However,absolute hermetic encapsulation cannot be achieved with organicadhesives, creating the risk, particularly at high relative humidity,that the base metals used as cathodes may corrode and/or thelight-emitting substances may be adversely affected.

[0013] Consequently, plasma thin-layer coating is preferable in allcases. For the following reasons, however, the standardized and knownmethods for plasma coating and producing pinhole-free barrier coatingsare not suitable for the coating of OLEDs:

[0014] A plasma is created when charged particles are accelerated to asufficient extent that the ionization energy of the gas or gas mixturebeing used is attained. In addition to ions and electrons, this producesphotons and excited species, all of which interact with the componentbeing coated. As a result of these interactions, the surface of thecomponent is chemically modified, which can already exert an adverseeffect on its properties. In addition, the ion bombardment leads to anincrease in the temperature of the component, which, in the case oforganic light-emitting diodes, can also lead to impairment of theperformance of the component following coating. In particular, however,radiation damage triggered by the photons present in the plasma must beviewed as the absolute exclusion criterion for the use ofplasma-supported processes in the coating of OLEDs.

[0015] This is all the more applicable since, in order to achievehermetically sealed coatings, the coating process must be performed atrelatively high plasma output levels and high self-bias (=large amountof ion energy) (cf. Klages et al., Surface and Coatings Technology,Elsevier: 1996, volume 90, Nos. 1-2, pages 121-128). Under theseconditions, the effects of the plasma on the OLED are especiallydisadvantageous.

[0016] The objective of the invention, therefore, is to provide aprocess for the coating of an electronic or microelectronic component bymeans of thin-layer coating, especially by means of plasma coating, inwhich no significant radiation damage to the component is caused. It isalso the objective of the invention to provide an OLED with a thin-layerencapsulation by means of plasma coating.

[0017] Thus, the object of the invention is a component comprising a

[0018] substrate,

[0019] an organic light-emitting diode disposed on the substrate and an

[0020] encapsulation,

[0021] wherein the encapsulation is produced in accordance with athin-layer process. In addition, the object of the invention is aprocess for encapsulating an electronic or microelectronic component bymeans of plasma coating, in which the reactivity of plasma-excitedparticles in the decay phase is utilized. The object of the invention isa process in which the plasma source is operated in a pulsed manner. Inaddition, the object of the invention is a process for encapsulating anelectronic or microelectronic component by means of a “remote” or “afterglow” process, in which plasma and the component to be coated arespatially separated from one another, thereby minimizing the interactionof the component with the accelerated ions and photons.

[0022] In both versions of the process, the critical requirement in itsexecution is to minimize the effects of the plasma on the component.There is a lower limit, or minimum output level for ignition of aplasma. However, the effectively utilized output for coating thecomponent at this minimum value can be further reduced by operating theplasma in a pulsed manner, or by placing the sample to be coated in theremote zone of the plasma.

[0023] For this reason, pulsed operation is also especiallyadvantageous, because the decay phase of excitation is effective interms of deposition. It takes place where or when the plasma is nolonger being excited. A “spatial” dark phase is found in remote areas ofthe plasma disposed at a great distance from the plasma source. A“temporal” “dark” phase exists between the pulses, i.e., the downtimesfor the excited output, as the serviceable lives of the light-emittingparticles are brief.

[0024] A “spatial” dark phase is found in remote areas of the plasmadisposed at a great distance from the plasma source. A “temporal” “dark”phase is found between the pulses, i.e., the downtimes for the excitedoutput, as the serviceable lives of the light-emitting particles arebrief.

[0025] As a result of the use of pulsed ECR (electron cylotronresonance) plasma, sensitive components in the electronics and/ormicroelectronics survive a thin-layer coating without damage and withvirtually unchanged characteristic curves (see FIGS. 1 to 3).

[0026] The plasma output to be set for coating purposes must be justabove the minimum output required to ignite the plasma. The period inwhich the plasma is activated is preferably about 20% of the entireduration of coating. Such coating processes have no measurable effect onthe characteristic curves of an OLED, even at a duration of one hour.

[0027] Organic monomers whose boiling point at a pressure of 1 bar isnot higher than 300° C. are preferably used as precursors for plasmadeposition. In principle, preference should be given to simplehydrocarbons, such as ethylene or methane,

[0028] as they are inexpensive and gaseous. In addition, the hydrogenhas a reducing effect, which is beneficial to the base cathode metals.The precursor for the remote or after glow processes is limited incomparison to coating in the pulsed, low-energy plasma. Economicallyfeasible deposition rates can only be achieved with comparativelyreactive precursors. Elevated reactivity, in this sense, is generallypresent when the precursor has at least one unsaturated bond.

[0029] Another critical issue in the execution of thin-layerencapsulation is adhesion, both between the OLED structure and theplasma coating and between the plasma coating and the subsequentbarrier. If the plasma coating does not reliably adhere to the OLED, thecoating can warp and cracks can develop. As a result, the subsequentlyapplied metal coating can come into electrical contact with the OLEDcathode, rendering the OLED unusable. To secure adhesion to the adjacentcoatings, and depending on the type of adjacent coating, it may benecessary to include functional groups in the plasma coating thatinteract with the adjacent coating. In this case, the use of purehydrocarbons is no longer productive; instead, heteroatoms must bepresent in the plasma coating. On the one hand, this can be achieved byusing a precursor that contains heteroatoms. However, the use ofprecursor mixtures is also possible. Preferably, at least one additionalprecursor is added to a pure hydrocarbon and serves as the heteroatomsource. This procedure is advantageous when different adjacent coatingssurround the plasma coating, as the type of heteroatom source can thenbe selected in such a way as to ensure optimal adhesion to each adjacentcoating. In this case, the heteroatom precursor is only added to theplasma during the coating process phase in which the boundary coating isproduced. Nitrogenous (amines, pyrroles) and sulfurous (SF₆ andthiophene) precursors

[0030] have proven to be advantageous.

[0031] The plasma coatings obtained by the method of the invention are,in principle, only slightly integrated and thus are not hermeticallysealed against the atmosphere. However, they are pinhole-free, thermallyconductive, and electrically insulating. This makes it possible to usevapor-deposited metal coatings as hermetically tight barriers.

[0032] If, in accordance with the present invention, the first coatingis selected to be sufficiently thick, an addition coating can be appliedby means of conventional plasma processes in continuous, i.e.,non-pulsed mode without adversely affecting the OLED. This is the casewhen the first coating protects the component to be coated against theeffect of the plasma and the temperature can, for example, be kept below100° C. with components that are only stable at temperatures below 100°C.

[0033] If additional mechanical protection of the component such as thatachieved with the “roof structure” (cf. DE 19943148.5) is desired, theencapsulation technology of the invention can be combined with such astructure.

[0034] The terms “remote” plasma and “after glow,” which refer to thesame thing, are known to the average person skilled in the art involvedin the respective field.

[0035] For execution purposes, commercially obtainable HDP sources (highdensity plasma sources) can be used, for example, if the accelerationvoltage directed to the substrate is switched off (bias power=0) and thedistance between the substrate and the plasma source is sufficientlylarge. A minimum distance of half the length of the plasma zone appearsto be advisable in this context.

[0036] The preferred distance between the plasma source and thesubstrate to be coated ranges between 20 and 70 cm, preferably between30 and 50 cm, with approx. 40 cm being especially preferable. [figure][x-axis] Voltage (V) [y-axis] Current density (A/cm²) [legend] beforeafter

[0037] Figure

[0038] OLED characteristic curve with an insufficient blockingcharacteristic, which is attributable to plasma damage, as indicated inthe literature and cited in the text. The terms “before” and “after”refer to the deposition of the plasma barrier coating. [figure] [x-axis]Voltage (V) [y-axis] Current density (A/cm²) [legend] before after

[0039] Figure

[0040] OLED characteristic curve with a blocking ratio at ±8 V suitablefor application. The difference between this characteristic and thatdepicted in FIG. 1 lies in the choice of the plasma parameters. Thischaracteristic demonstrates that damage to the OLED coating by theplasma can be avoided through suitable process control. [figure][x-axis] Voltage (V) [y-axis] Efficiency (cd/A) [legend] before after

[0041] Figure

[0042] The characteristic curves exhibit constant efficiency across avoltage range of up to 10 V. This efficiency is insignificantly reducedby covering the OLED with the barrier plasma coating (“after”).

1. Component comprising a substrate, an organic light-emitting diode disposed on the substrate and an encapsulation, wherein the encapsulation is produced in accordance with a thin-layer process.
 2. Component according to claim 1, which comprises at least one second coating for encapsulation of the OLED.
 3. Component according to claim 2, in which an additional coating is a vapor-deposited metal coating.
 4. Component according to claim 2 or 3, in which an additional coating is a coating produced by means of a conventional plasma process.
 5. Component according to one of claims 2 to 4, in which an additional coating is a roof structure.
 6. Process for encapsulating an electronic or microelectronic component by means of plasma coating, in which the plasma source is operated in a pulsed manner.
 7. Process for encapsulating an electronic or microelectronic component by means of a “remote” or “after glow” process, in which plasma and the component to be coated are spatially separated from one another.
 8. Process according to claim 7, in which the spatial distance between the plasma source and the substrate to be coated is approx. 40 cm.
 9. Process for encapsulating an electronic or microelectronic component according to one of claims 6 to 8, in which the period in which the plasma is activated is approx. 20% of the entire duration of coating.
 10. Process for encapsulating an electronic or microelectronic component according to one of claims 6 to 9, in which at least one precursor for the plasma deposition is an organic monomer.
 11. Process for encapsulating an electronic or microelectronic component according to claim 10, in which the boiling point of the monomer at a pressure of 1 bar is not higher than 300° C.
 12. Process for encapsulating an electronic or microelectronic component according to one of claims 6 to 10, in which at least one precursor, which is a hydrocarbon such as ethylene and/or methane, is used.
 12. [sic] Process for encapsulating an electronic or microelectronic component according to one of claims 6 to 11, in which at least one precursor has at least one unsaturated bond.
 13. Process for encapsulating an electronic or microelectronic component according to one of claims 6 to 12, in which at least one precursor is used which features at least one functional group that interacts with the adjacent coating.
 14. Process for encapsulating an electronic or microelectronic component according to one of claims 6 to 13, in which at least one precursor has at least one heteroatom.
 15. Process for encapsulating an electronic or microelectronic component according to claim 14, in which at least one heteroatom is a nitrogen and/or a sulfur atom.
 16. Process for encapsulating an electronic or microelectronic component according to one of claims 14 or 15, in which at least one precursor is an organic monomer selected from the group consisting of amines, pyroles, sulfur fluorides and thiophenes.
 17. Process for encapsulating an electronic or microelectronic component according to one of claims 6 to 16, which is used in combination with a vapor-deposited metal coating, a conventional plasma coating and/or a roof structure. 